Starting around mid-August through September, both the Western Monarch and Eastern Monarch butterfly populations (Danaus plexippus) begin their long journey south from southern Canada and northern USA to their overwintering sites in coastal California and Mexico. These magnificent, colorful creatures are the world's most recognized and beloved butterflies.  Yet, they are increasingly in danger of becoming extinct.

Life Cycle

Like all butterflies, Monarch butterflies have four life stages: 

• Egg: The female Monarch lays her eggs on their sole host plant, the milkweed (Asclepias). She generally lays one egg per plant.  Each egg is about the size of a grain of salt. 
• Larva (Caterpillar):  After 3 – 5 days, the Monarch egg hatches to a larva, also called a caterpillar, eating only milkweed leaves. They go through five instar stages over a period of 10 – 14 days as they grow from 1/16^th of an inch to about two inches, molting their exoskeleton at each stage.
• Pupa: The caterpillar finds a protected place to develop its chrysalis for the pupal stage. During the next 11-15 days the pupa will change to an adult by liquifying its body while inside the chrysalis, ultimately emerging to the adult butterfly.
• Adult: In the final hours before emergence, the chrysalis becomes translucent, a crack will appear, with the Monarch butterfly freeing itself from the case. Hanging from the now-empty chrysalis case, it will spend the next few hours pumping fluid into its wings until they are firm enough to fly. Eventually it will take flight and start seeking out nectar for its 1^st meal. Adult Monarch butterflies feed on flowers, which makes them pollinators. The nectar provides energy for flight, mating, and migration.

Milkweed

Milkweeds are herbaceous, perennial, flowering plants, named for their latex, a milky substance, which is exuded when the plant is damaged. It is potentially toxic to humans and many other species.  Monarchs have evolved the ability to store the toxins. Caterpillars feeding on milkweed retain the poison as chrysalids and adults. Birds and other Monarch predators dislike the toxins and learn to avoid them. (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19440).

Migration

The Monarch migration is extraordinary with none quite like it in the butterfly world. A Monarch butterfly begins an epic one-way journey south up to 2,800 miles to a specific place where they have never been to before, where their great-grandparent spent the previous winter. It remains largely a mystery how successive generations know the route and where to spend the winter months.

No single Monarch makes the entire round trip journey north and south. There are four to five generations each year. Three to four generations make the journey north in the spring and summer months, with each generation moving further north.  Each northward generation consists of adults feeding on nectar, mating, females laying eggs on milkweed, the parents dying, their offspring hatching from eggs, going through the larval and pupal stages, ultimately becoming adults, and continuing the cycle. The adults in these generations live two to six weeks.

Late in summer or early fall, a final generation emerges.  Triggered by changes in temperature and sunlight, this generation will migrate south. Known as the “Methuselah” generation (after the biblical patriarch said to have lived 969 years), they can live up to 6 – 8 months. They do not emerge as sexually mature butterflies, being in a “sexual diapause,” so their energies can be focused on developing flight muscles and storing lipids for their long journey south and surviving the winter months.

Come spring, with warming temperatures and longer days, these butterflies will become sexually mature, feed on nectar, mate, and start moving northward, laying eggs, which will hatch to continue the annual migration cycle.

You may see migrating Monarchs this fall in your garden feeding on nectar flowers, resting on flat flowers or rocks, or drinking from water sources.  Admire them, but leave them be, since they still have some distance to go to reach their wintering grounds. In California, their wintering spots are along coastal areas from Monterey area (Pacific Grove) to San Diego.

Monarchs in Trouble

On July 21 of this year, the International Union for Conservation of Nature (IUCN) announced the Monarch butterfly has been put on its "Red List of Threatened Species as Endangered” due to habitat destruction, climate change, and pesticides, with the primary reason being reduction in milkweed plants that are so vital to their survival.

In temperate areas like the Central Valley, the tropical milkweed plant (Asclepias currasavica) does not go dormant. A parasite that lives on the plant is ingested by developing caterpillars and is linked lower migration success and reductions in lifespan. Choose milkweed species that goes through winter dormancy such as narrowleaf milkweed and showy milkweed (A. fasicularis and speciosa.) 

The IUCN announcement states: "The western population is at greatest risk of extinction, having declined by an estimated 99.9%, from as many as 10 million to 1,914 butterflies between the 1980s and 2021.” In addition, "The larger eastern population also shrunk by 84% from 1996 to 2014. Concern remains as to whether enough butterflies survive to maintain the populations and prevent extinction."

Sign up for our Free Class!

On Saturday, October 15, UCCE Stanislaus County Master Gardeners Rhonda Allen and Denise Godbout-Avant will give a talk on these marvelous butterflies that so many love. Learn about butterflies in general, more about Monarchs, their life cycle and their incredible migration, the importance of nectar plants and milkweed to their survival, and how you can help them. Free milkweed seed packets will be given to attendees.  Use the link below to register.

Date: Saturday, October 15, 2022
Time: 9:00 am – 10:30 am
Where: Stanislaus Agricultural Center, 1800 Cornucopia Way, Harvest Hall 
Register: http://ucanr.edu/monarchs/2022

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Resources:

• Art Shapiro's Butterfly Site   https://butterfly.ucdavis.edu/butterflies 
• Butterflies in Your Garden  https://ucanr.edu/sites/CEStanislausCo/files/345791.pdf
• Xerces Society - Pollinator Plants: California  https://xerces.org/publications/plant-lists/pollinator-plants-California
• UC Davis Arboretum – Larval Hosts for Butterflies https://arboretum.ucdavis.edu/blog/larval-host-plants-butterflies
• California Native Plant Society – Native Planting Guides https://www.cnps.org/gardening/choosing-your-plants/native-planting-guides
• Tropical Milkweed - a no grow  https://xerces.org/blog/tropical-milkweed-a-no-grow 
• Calscape CA native plants     https://www.calscape.org/
• UC ANR Bug Squad Blog     https://ucanr.edu/blogs/bugsquad/
• International Union for Conservation of Nature (IUCN)  https://www.iucn.org/
• The Monarch: Saving Our Most Beloved Butterfly, by Kylee Baumle, St. Lynn's PressMilkweed Poisoning: https://www.poison.org/articles/milkweed-can-cause-serious-poisoning-204